The present invention relates to a technique for suppressing oscillation of an actuator head suspension assembly in a rotating disk storage device such as a magnetic disk drive or a magneto-optic disk drive and more particularly to a technique for suppressing fluttering of an actuator arm caused by an air flow generated on a surface of a rotating disk.
A magnetic disk drive as an example of a rotating disk storage device includes a magnetic disk, which has a magnetic layer formed on a surface thereof and is adapted to rotate about a spindle shaft, an actuator head suspension assembly (hereinafter referred to as “AHSA”), and a control unit for controlling the transfer of data and the operation of the device. The AHSA includes a head suspension assembly (hereinafter refer to as “HSA”) and an actuator assembly. The HSA includes a head which makes access to the magnetic disk for performing both or one of read and write of data, a slider to which the head is attached and which is provided with an air bearing surface (hereinafter refer to as “ABS”), a spring structure called flexure to which the slider is attached, and a load beam which supports the flexure. The actuator assembly includes an actuator arm which supports the HSA, a voice coil which constitutes a voice coil motor (hereinafter refer to as “VCM”), a coil support which holds the voice coil, and a pivot bearing housing.
A head/slider constituted by a head and a slider floats by an extremely slight height on the surface of the magnetic disk which is rotating, while being supported by the flexure and performing a pivotal motion, and is positioned to a predetermined track position, then is controlled so as to perform a follow-up operation for tracks. Servo information is recorded in each track. The control unit calculates an error between a target position and the present position from the servo information read by the head and then controls the VCM so that the head floats centrally of a track, while allowing the AHSA to perform a correcting operation. If the head should undergo an unexpected displacement due to, for example, oscillation or shock while the control unit makes a positional control for the head, a longer time than necessary may be consumed until the head is positioned to a predetermined track, or the head may access an erroneous track.
With improvement in recording density of the magnetic disk drive, the accuracy required at the time of positioning the head to a predetermined track is becoming increasingly strict. In the magnetic disk drive, an air flow, which is created on the surface of the magnetic disk so as to advance in the rotating direction of tracks with high-speed rotation of the disk, is utilized for imparting buoyancy to the slider. While the head reads or writes data, the air flow created on the disk surface collides with the ASHA and causes a change in flow velocity. A natural oscillation is usually developed in the actuator arm which is driven by the VCM. If a change in flow velocity of the air flow occurs in the vicinity of the actuator arm, the amplitude of the natural oscillation increases and an oscillation called arm fluttering results, which affects the positional control for the head.
Displacement modes caused by oscillation of the actuator arm there include bending, sway, and torsion. Bending is a displacement of the actuator arm in a direction perpendicular to the surface of the magnetic disk. Sway is a displacement in the pivoting direction of the actuator arm. Torsion is a displacement in a direction rotating about a virtual center line extending in the longitudinal direction of the actuator arm. The larger the number of revolutions of the magnetic disk, the higher the velocity of the air flow and the more marked the arm fluttering. Further, the larger the number of stacked magnetic disks, that is, the larger the number of actuator arms, the greater the influence of the air flow exerted on the whole of the AHSA and the more marked the arm fluttering.
As a track pitch has recently been becoming increasingly narrow in quick tempo, the necessity of preventing arm fluttering has become stronger than before. In addition, it has been proposed to increase the number of magnetic disks to be stacked for the purpose of increasing capacity or increase the number of revolutions of the magnetic disk for the purpose of improving the access speed. With these as background, the prevention of arm fluttering is becoming an important issue. U.S. Pat. No. 5,446,612 and U.S. Published Patent Application No. 2003-16473 disclose techniques for suppressing the disturbance of an air flow to suppress fluttering caused by an actuator arm.
FIG. 1 is a perspective view of a conventional AHSA 10. The AHSA 10 includes a pivot bearing housing 11, a coil support 14, a voice coil 16, an actuator assembly composed of actuator arms 12a to 12d, and HSAs 18a to 18f connected to the actuator assembly. In the same figure, four actuator arms 12a to 12d are stacked. When the head accesses a magnetic disk, the disk is in a rotating condition between adjacent actuator arms. One set of HSA is connected to each of the top and bottom actuator arms, while two sets of HSAs are connected to each of the other two actuator arms 12b and 12c which are stacked inside. Therefore, the actuator arms 12a to 12d are each influenced by an air flow created on the surface of a magnetic disk opposed thereto.
Each of the actuator arms 12a to 12d is formed with three balance apertures 5, which are for taking the balance of the entire weight of the AHSA centered on a pivot shaft. That is, by setting the center of gravity of the AHSA on the pivot shaft, even if a shock which involves a parallel movement is given to the magnetic disks from the exterior, the AHSA is prevented from pivoting to minimize the influence on the positioning accuracy. Further, the operation characteristic of the AHSA is improved by taking the weight balance.